To dock with the Salyut station was a four-stage automated process over which the cosmonauts had no control. The first stage was the initial mechanical contact, when the head of the active spacecraft’s probe touched the interior of the conical drogue. This activated a sensor in the shock absorber on the probe. Then stabilisation thrusters were to slowly force the ship forward to drive the head of the probe into the hole at the apex of the cone, which the engineers referred to as the ‘nest’. When the head of the probe penetrated the nest, this initiated the capture stage, and latches in the nest engaged the probe in order to prevent it slipping out. The Apollo spacecraft had a similar system, and American astronauts refer to this as a ‘soft docking’. The third stage involved retracting the probe to draw the two annular collars together, to engage latches which would form a rigid bond and establish electrical and hydraulic connections located around the external rim – a status that astronauts refer to as a ‘hard docking’. Then the probe would release its head, which would remain in the nest while the ‘beheaded’ probe withdrew into the housing on the nose of the orbital module. Once air had been introduced to the hermetic tunnel and the seals verified, the cosmonauts could swing back the hatch, complete with the docking assembly, to enter the tunnel and then swing the drogue into the station.
In the case of Soyuz 10, the problem struck between the second and third stages – during the retraction, 9 minutes after the first contact. The only physical connection was the head of the probe in the nest. However, owing to an oversight in planning, the control system of the Soyuz spacecraft was still operating and when this noticed an early deviation in attitude it fired the thrusters in an effort to eliminate the ‘error’. If the spacecraft had been free, these impulses would have conformed to the logic of the control system; but it was not free – its probe was confined by the drogue. Upon finding that the spacecraft did not conform to its logic, the control system started to fire the thrusters on a continuous basis in an effort to assert its authority, and this subjected the probe to dynamic forces sufficiently strong to break one of the four
levers surrounding its base. The probe was designed for a maximum force of 80 kg, but survived a load of 160-200 kg before failing.
The first error in the design of the docking process was to leave the spacecraft’s control system active after the initial capture, because the conditions required by its logic no longer applied. The second error was to make the docking sequence fully automated once it had been initiated by the mechanical contact. Yeliseyev, who had participated in the development of the control system, had realised that the control system was jeopardising the docking process, but had no way to intervene – he was a frustrated spectator.
As Soyuz 10 was a 7K-T spacecraft designed to operate as a space station ferry, it carried air, water and food for just 3 days of autonomous operations. There was no option but to return to Earth as soon as possible.
The task was to separate from the station in a manner that would not damage the drogue. In designing the undocking process it had been assumed that the docking would have been finished and that commands could be directed through the circuits in the collars – which was impossible in this case. What would normally occur was that after the crew had left the station they would seal the Soyuz hatch and then command the latches to release the head of the probe from the nest so that the spacecraft could fire its thrusters to withdraw. However, in this unpredicted situation it was possible that the mechanism would fail to release. Indeed, the first attempt failed, and when Shatalov fired the thrusters his spacecraft simply swung around on its damaged probe.
In the control room General Andrey Karas, the Commander of Space Assets in the Strategic Rocket Forces, said bitterly: “Well, congratulations. You’ve developed a docking system in which ‘mom’ doesn’t release ‘dad’!’’
There were two emergency options: one to cut loose the docking mechanism from the nose of the orbital module, and the other to release the orbital module itself. In both cases the only access point to Salyut would be left fouled.
Afanasyev of the Ministry of General Machine Building issued a directive: ‘‘This ‘amputation’ is not suitable. What do you want? To lose the first orbital station? Search for a method by which to deceive your super-clever scheme.’’
Salyut was saved by Zhivoglotov, the engineer who had appalled the control room by outlining eight possible reasons for the docking failure. After Zhivoglotov had outlined his plan, instructions were read up to Rukavishnikov who, during the 84th revolution, once again entered the orbital module and reconnected a number of the cables to deceive the mechanism into thinking that the release command came from Salyut. The command was issued on the next revolution by the cosmonauts using their command panel – and the latches released the head of the probe! At 10.17 a. m., after 5 hours and 30 minutes of drama, and during the 5th revolution spent in a soft – docked configuration, Soyuz 10 withdrew from the station. The news prompted loud applause in the TsUP. Although Soyuz 10 had not achieved its main objective of boarding Salyut, everyone hoped that the station was undamaged and therefore would be available to a future mission.
For almost half an hour Soyuz 10 flew in formation with Salyut, with Shatalov manoeuvring while his colleagues inspected and photographed the docking system.
Few of these black-and-white pictures were published, and those that were released were of a poor quality. Nor was the television from the spacecraft during this period released. On Saturday, 24 April, Moscow TV declared that the docking had taken place and showed a 30-second clip which was said to be from an automatic camera on Salyut as Soyuz 10 withdrew. The Earth was in the background. The only part of the station that was visible was just in front of the camera, and was brilliantly white. The docking was portrayed as having been successful, with the link-up being only a test in an ongoing programme – there was no suggestion that the cosmonauts were to have entered the station.